In recent years, a piezo-electric actuator attracts attention in a portable information device field, and chemistry and medical fields as a new motor, which replaces an electromagnetic motor, in that miniaturization and high densification of a motor are allowed. The piezoelectric actuator does not generate an electromagnetic noise on the occasion of its drive, and, is not influenced by noise. Furthermore, the piezoelectric actuator attracts attention as a part of making such equipment with submillimeter class size that is represented by a micromachine, and a minute piezoelectric thin-film element is requested as its drive source.
As for a piezoelectric material used for a piezoelectric element, generally, it is common to obtain by finely forming a sintered compact or a single crystal member as a bulk material, which is given heat-treatment so as to obtain characteristics as a piezoelectric substance, in desired size and thickness with technology such as machining and polishing. In addition, when forming a minute piezoelectric thin-film element, a method of directly forming the piezoelectric thin-film element by coating and calcining a green sheet-like piezoelectric substance by using methods, such as a printing method, in a predetermined position on a substrate, such as metal or silicon is common. A thickness of such a compact from a green sheet is tens to hundreds of μm, electrodes are provided in upper and lower sides of the piezoelectric substance, and a voltage is applied through the electrodes.
Heretofore, a small piezoelectric element which was used for a liquid discharge head was produced by finely forming a piezoelectric substance as a bulk material with technology such as machining or polishing as mentioned above, or using a green sheet-like piezoelectric substance. As a device using such a piezoelectric thin-film element, for example, there is a liquid discharge head which has unimorph type piezoelectric thin-film element structure. The liquid discharge head is equipped with a pressure chamber communicating with an ink feed chamber, and an ink discharge orifice communicating with the pressure chamber, and a diaphragm with which the piezoelectric element is bonded or in which it is formed directly is provided and composed in the pressure chamber. In such construction, an ink droplet is discharged from the ink discharge port by compressing the ink in the pressure chamber by generating flexural vibration, which is caused by expanding and contracting the piezoelectric element by applying a predetermined voltage to the piezoelectric element.
Although color ink jet printers have spread presently by using such an operation of the above-mentioned piezoelectric substance, enhancement in their printing performance, and in particular, higher resolution, and high speed printing are requested. Therefore, it has been attempted to attain high resolution and high speed printing using multi-nozzle head structure in which a liquid discharge head has been miniaturized. In order to miniaturize a liquid discharge head, it is necessary to miniaturize further a piezoelectric element for discharging ink.
Furthermore, recently, attempts of applying liquid discharge heads to industrial applications such as straight writing of wiring have been also active. At that time, it is necessary to pattern liquid with more various characteristics on a processed surface at higher resolution, and hence, further high performance of a liquid discharge head is requested.
In recent years, because of development of micromachine technology, researches of developing a highly precise micro piezoelectric element by forming a piezoelectric substance as a thin film, and using fine processing technology having been used in semiconductors have been performed. In particular, a thickness of a piezoelectric film formed by film methods, such as a sputtering method, a chemical vapor deposition method, a sol gel method, a gas deposition method, and a pulsed laser deposition method is generally hundreds of nm to tens of μm in the case of an application to a piezoelectric actuator. Electrodes are provided to this piezoelectric film and a voltage is applied through these electrodes.
On the other hand, researches of high performance piezoelectric materials, having larger piezoelectric property, in connection with miniaturization of a piezoelectric element are also active. Generally, when an electric field is applied in a direction of intrinsic polarization of a monocrystalline piezoelectric substance, it is considered that high piezoelectric characteristics are obtained, but researches of performing domain control called domain engineering as one method of enhancement in piezoelectricity of a piezoelectric substance have been performed recently. For example, as a relaxer monocrystalline piezoelectric substance, {Pb(Zn1/3Nb2/3)O3}1-x—(PbTiO3)x (lead zinc niobate-lead titanate: PZN-PT) is known. In this relaxer monocrystalline piezoelectric substance, drastic improvement of a piezoelectric constant by performing domain control is reported. That is, in “Ceramics Vol. 40, (8), 2005, P. 600 (reference 1: Non-Patent Document 1), it is reported that the piezoelectric constant of 30 times or more (2500-2800 pC/N) of a piezoelectric constant d33 in a spontaneous polarization direction is obtained in this material.
In addition, a relaxer-based monocrystalline piezoelectric substance that is represented by, for example, {Pb(Mg1/3Nb2/3)O3}1-x—(PbTiO3), (lead magnesium niobate-lead titanate: PMN-PT) shows excellent piezoelectricity in particular. In U.S. Pat. No. 5,804,907 specification (Patent Document 1), it is described that large piezoelectricity is obtained when an electric field is applied in a <001> direction of a PMN-PT monocrystalline piezoelectric substance. This piezoelectricity is achieved by adjusting composition to a pueudo cubic side near a morphotropic phase boundary (MPB) between a tetragonal and a pueudo cubic of PMN-PT which is generally said for piezoelectricity to be good, and applying a voltage to the <100> direction. This is illustrated in a phase diagram of FIG. 2b in the patent.
These are considered that a relaxer single crystal material expresses large piezoelectricity by using phase transformation (rhombohedral, pueudo cubic ->tetragonal) of the reversible crystal following an application of an electric field by domain engineering generally called engineered domain structure.
Nevertheless, generally, such a monocrystalline piezoelectric substance is synthesized by flux melting of PMN-PT as described in Japanese Patent No. 3,397,538 specification (Patent Document 2). Such bulk state of piezoelectric substance needs to be given fine formation by techniques, such as machining and polishing, as described above, and hence, an application to a highly accurate micro piezoelectric element is hard.
Then, forming such a piezoelectric substance as a film using film methods, such as sputtering method, a chemical vapor deposition method, a sol gel method, a gas deposition method, and a pulsed laser deposition method, has been investigated. In the following documents, it is reported that a PMN-PT thin film was formed as a film by the PLD method. —Applications of Ferroelectrics, 2002, ISAF 2002, proceedings of the 13th IEEE International Symposium P133-136 (Non-Patent Document 2). Nevertheless, even if it is the above-mentioned piezoelectric highly piezoelectric material, when a piezoelectric film is formed by a thin film forming method using it, such high piezoelectricity that is originally expected has not been achieved yet.
On the other hand, as represented by Pb(ZrxTi1-x)O3 (lead zirconate titanate: PZT), Japanese Patent Application Laid-Open No. H08-116103 (Patent Document 3) describes a method of controlling crystal orientation to a monocrystalline (001) when a material which shows excellent ferroelectricity, pyroelectricity, and piezoelectricity is formed by a thin film forming method. Japanese Patent Application Laid-Open No. 2000-332569 (Patent Document 4) and U.S. Pat. No. 6,198,208 specification (Patent Document 5) propose a method of using 90-degree domains where orientation (100) and orientation (001) of tetragonal structure are intermingled. Nevertheless, since a MPB region with good characteristics cannot be used in the above-mentioned method, such high piezoelectricity that is originally expected has not been achieved yet.